Cleaning methods for the isotopic determination of diatombound nitrogen in non‐fossil diatom frustules

Morales, Laura V.; Sigman, Daniel M.; Horn, Matthew; Robinson, Rebecca S.

doi:10.4319/lom.2013.11.101

Cited by 27 publications

(21 citation statements)

References 31 publications

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“…The δ 15 N db difference that characterizes the centric and pennate diatom assemblages may indicate (1) a difference in seasonality or depth habitat, as it affects the δ 15 N of the available nitrate, (2) differences in the dominant form of N assimilated (i.e., nitrate or recycled ammonium) [ Fawcett et al ., ], or (3) physiological differences that result in a different δ 15 N db /diatom biomass δ 15 N relationship [ Horn et al ., ; Morales et al ., ]. Regarding the last, if the centric‐pennate δ 15 N db difference were solely due to differences in fundamental biosynthesis pathways as they impact the δ 15 N relationship between the biomass N of a diatom and its frustule‐bound N, then a constant interassemblage difference would be expected over time.…”

Section: Interpretation and Discussionmentioning

confidence: 99%

Antarctic Zone nutrient conditions during the last two glacial cycles

et al. 2015

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In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom-bound N isotope (δ 15 N db ) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ 15 N db (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal-and barium-based proxies for reduced export production during ice ages, the δ 15 N db increases point to ice age reductions in the supply of deep ocean-sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ 15 N db changes are not the result of changing species composition. The pennate and centric assemblage δ 15 N db records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality-based interpretation of the centric-to-pennate δ 15 N db difference suggests that late summer surface waters became nitrate free during the peak glacials.

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Section: Interpretation and Discussionmentioning

confidence: 99%

Antarctic Zone nutrient conditions during the last two glacial cycles

et al. 2015

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“…Physically separated diatom samples were cleaned using (1) a preliminary oxidation of external organic matter using ~5 ml of 18 M sulfuric acid, ~15 ml saturated potassium permanganate, and ~15 ml saturated oxalic acid [ Hasle and Fryxell , ], (2) a reductive cleaning step using a heated (80°C for 1 h) sodium dithionite solution to remove adsorbed metals, and (3) two final 1 h oxidations of organic matter using a weak (~35%) and then strong (72%) solution of perchloric acid in a 100°C water bath [ Horn et al, ; Morales et al, ]. Splits of the clean, dry diatom samples were dissolved and the organic N oxidized to nitrate in a 0.22 M potassium persulfate and 1.5 M sodium hydroxide solution in an autoclave at 121°C for 20 min [ Bronk et al, ; Robinson et al, ].…”

Section: Methodsmentioning

confidence: 99%

The changing roles of iron and vertical mixing in regulating nitrogen and silicon cycling in the Southern Ocean over the last glacial cycle

et al. 2014

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The Southern Ocean plays a critical role in the air-sea CO 2 balance through biological and physical mechanisms. Vertical supply of deep waters returns nutrients and CO 2 to the surface and stimulates phytoplankton growth. Photosynthesis in the Southern Ocean is limited by iron and only a fraction of the carbon and nutrients that return to the surface are consumed for potential sequestration in the deep sea. Here we present the most spatially extensive data set of silicon and nitrogen isotope measurements from diatom frustules to date to examine the controls on nutrient drawdown during the last glacial period and across the glacial termination in both the Antarctic and Subantarctic zones. The new data confirm existing views that differing silicon and nitrate consumption patterns in the Antarctic zone are likely the result, at least in part, of iron addition during the last glacial maximum (LGM). However, earlier in the glacial, a more coordinated response in the two proxy records, with both reflecting enhanced consumption during episodes of increased iron accumulation and export production, implies a different system response than observed for the LGM. A collapse of the expected equatorward gradient in silicon isotope values and contraction of the nitrogen isotope gradient during the deglaciation suggests that nutrient supply increased not only in the Antarctic Zone, but also in the Subantarctic, perhaps due to enhanced deep mixing locally. Enhanced deep water ventilation across the Southern Ocean likely increased the nutrient content of mode waters during the deglaciation.

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“…It has been shown that Thalassiosira pseudonana frustules contained hydrocarbons, protein and lipids after a H2O2 treatment [35] . Furthermore, H2O2 treatment removed more elements from the frustules than SDS/EDTA [34] , and facilitated the access to N embedded in the biosilica [33] . These observations may influence the choice of cleaning methods for frustules that are subjected to elemental analyses.…”

Section: Sem/eds and Element Analysismentioning

confidence: 99%

“…acids, bleaching, oxidising or denaturation functions from different chemicals, and thermal treatment. There are few systematic studies with comparisons of different cleaning methods [30] , [31] , [32] , [33] , [34] . Here, a comparative study of two frustule cleaning methods is presented, using carefully described cleaning protocols based on established cleaning principles [35] .…”

Section: Introductionmentioning

confidence: 99%

Diatom frustules as a biomaterial: effects of chemical treatment on organic material removal and mechanical properties in cleaned frustules from two Coscinodiscus species

et al. 2016

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The three-dimensional structure of silica diatom frustules offers a great potential as nanoporous material for several nanotechnological applications, but the starting point for these applications is the ability to obtain clean frustules with sufficient mechanical strength and intact structure. Here, frustules from the diatoms Coscinodiscus centralis Ehrenberg and C. wailesii Gran et Angst are characterized with respect to their structural integrity, content of residual organic biomaterial and their mechanical properties after two cleaning methods using either hydrogen peroxide as oxidizing agent or a combination of a surfactant (sodium dodecyl sulphate) and a complexing agent. Fluorescence microscopy and energy dispersive spectroscopy (SEM/EDS) analysis revealed clear differences regarding the amount of organic residual within the frustules depending on the cleaning process, with little organic material left after the oxidizing method. This method, however, induced a partial cracking of the frustules suggesting an embrittlement due to the cleaning. Nanoindentation confirmed this and showed that the oxidizing method resulted in more brittle frustules compared to the surfactant/complexing method. More efficient cleaning of organic biomaterial may result in more fragile frustules, and the choice of cleaning method must be based on the planned application.

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Cleaning methods for the isotopic determination of diatombound nitrogen in non‐fossil diatom frustules

Cited by 27 publications

References 31 publications

Antarctic Zone nutrient conditions during the last two glacial cycles

Antarctic Zone nutrient conditions during the last two glacial cycles

The changing roles of iron and vertical mixing in regulating nitrogen and silicon cycling in the Southern Ocean over the last glacial cycle

Diatom frustules as a biomaterial: effects of chemical treatment on organic material removal and mechanical properties in cleaned frustules from two Coscinodiscus species

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